LOS ANGELES  Two more companies are jumping into the mobile streaming music field with applications that work on iPhones, giving consumers new ways to listen to millions of tracks on the go for about $10 a month.

Music blog site MOG and a start-up called Rdio, backed by Skype co-founders Niklas Zennstrom and Janus Friis, are both entering a market already served by Rhapsody and Thumbplay.

These so-called "cloud music" services do away with the need to download songs because the mobile devices tap into songs stored on distant computers through the cellphone network.

In that way, they are the latest to challenge Apple's grip on selling music as downloads through its iTunes store.

On Monday, a different start-up called mSpot also launched to the public as a "beta" test, giving users a way to store music they already have and stream it to themselves on mobile devices. It's free for 2 gigabytes of music, or about 1,600 songs; monthly fees are charged beyond that.

Along with access to 7.5 million tracks, MOG touts a slider control that gradually changes how many randomly selected tracks come from a single artist or many similar ones.

MOG's iPhone app was approved last week, and MOG plans to launch in July on iPhones and on mobile devices that use Google's Android operating system.

Also this summer, MOG is launching an application on the Roku set-top box, which was made popular for its integration with movie service Netflix.

That application will allow subscribers to listen to songs through their TV and computer for about $5 per month. (The $10-a-month plan for phones includes Roku and computer access.)

"It's part of our vision and our strategy to integrate MOG in all these experiences," said Drew Denbo, MOG's senior vice president of business development.

Rdio, with 5 million songs, is focused on social networking, with a splash page on the website that shows what your friends are listening to and what they think about it.

The fee structure is similar, with about $10 per month giving users access to songs on their Blackberry devices or iPhones. The company plans to roll out on Android devices later. For about $5, users can listen to Rdio songs on a computer.

Rdio launched in an invitation-only paid preview program in early June.

Friis, who sold the Internet-based phone service Skype to eBay for more than $2.6 billion in 2005, said he's not worried that the mobile music field now has so many start-ups as competitors.

Apple is also expected to launch its own service for accessing music remotely, following the company's purchase of the music start-up Lala.

"It's fundamentally always about creating the best product. That's what we think we did with Skype and that's why it took off," Friis said. "This is the very, very early start of a whole new phase of music consumption. We think now is the right time."

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